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Serology-informed estimates of SARS-CoV-2 infection fatality risk in Geneva, Switzerland

Our take —

This study based on seroprevalence data and modeling from Geneva Switzerland, available as a preprint and thus not yet peer-reviewed, confirms previous studies which have shown that the infection fatality ratio increases with age, and increases sharply after 65 years of age.

Study design

Modeling/Simulation

Study population and setting

The authors estimated the overall and age-specific infection fatality risk (IFR) for Geneva Switzerland using daily case and death reports between February 24 and June 2, 2020, combined with five weekly seroprevalence estimates starting April 6, 2020. The authors linked the sources of information to be able to infer IFR, and used Bayesian methods to account for the lag between infection and seroconversion, and between infection and death.

Summary of Main Findings

There were 286 total COVID-related deaths from February 2 to June 2, 2020 in Geneva. The IFR was low among those under 50 years of age at between 0.00032 and 0.0016% but this increased to 0.14% (95% Credible Interval (CrI) 0.096-0.19) among those 50-64 years, and to 5.6% (95% CrI 4.3-7.4) for those 65 years or older. The authors estimated the population-wide IFR to be 0.64% (95% CrI 0.38-0.98). When cases and deaths among care home residents were excluded from the analysis, the estimated IFR was 2.7% (95% CrI: 1.6 – 4.6) for those 65 years or older.

Study Strengths

The study was focused on a specific geographic area (Geneva) which allowed for more complete data of cases and deaths. This was matched with data from sequential seroprevalence surveys from a representative population.

Limitations

The focus on a distinct geographic location may limit the generalizability of the findings outside of Geneva. In the older population (65 years +), half of the deaths were among nursing home residents, but such residents are likely underrepresented in the sero-survey data used to create the estimates, which could bias the results, likely by overestimating the IFR in this group. Finally, if antibody responses differ by disease severity with milder cases having a weaker and shorter response, authors’ estimates of IFR may be biased upwards.

Value added

This study provides additional information on the modeled infection fatality risk (IFR) underpinned by seroprevalence data to add to the small but growing literature on IFR. A diversity of IFR estimates will be needed given that it is likely to differ from one population to another. It also highlights the disproportionate number of deaths in vulnerable settings such as care homes.

This review was posted on: 15 July 2020